Fuel cell and separator thereof

ABSTRACT

A fuel cell includes a plurality of fuel cell units, each fuel cell unit including an electrode assembly formed by disposing electrodes on both sides of an electrolyte, a pair of separators that sandwich the electrode assembly, and gas sealing members that are disposed at an outer peripheral portion of the electrode assembly, and that seal respective reaction gas flow passages that are formed between each separator and the electrode assembly. In one of the separators of each of the fuel cell units, a through path is formed that penetrates the separator in the thickness direction thereof, and the through path formed in one of the separators of one of the fuel cell units and the through path formed in one of the separators of adjacent one of the fuel cell units are offset with each other as viewed in the thickness direction of the separators.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of application Ser. No.11/080,889, now U.S. Pat. No. 7,632,597, which is a divisionalapplication of application Ser. No. 10/328,878, which is now U.S. Pat.No. 6,866,959, filed Dec. 24, 2002, and claiming priority on JapanesePatent Application No. 2001-393620, filed Dec. 26, 2001, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell formed by stacking aplurality of fuel cell units that are formed by sandwiching an electrodeassembly between separators, and also to a separator of a fuel cell.

2. Description of the Related Art

Among fuel cell units, there is one type that is formed in a plate shapeby sandwiching between a pair of separators an electrode assembly thatis formed by placing an anode electrode and a cathode electroderespectively on either side of a solid polymer electrolyte membrane. Afuel cell is formed by stacking in the thickness direction of the fuelcell units a plurality of fuel cell units that are structured in thisway.

In each fuel cell unit there is provided a flow passage for fuel gas(for example, hydrogen) on the surface of the anode side separator thatis positioned facing the anode electrode, and there is provided a flowpassage for oxidizing gas (for example, air that contains oxygen) on thesurface of the cathode side separator that is positioned facing thecathode electrode. In addition, a flow passage for a cooling medium (forexample, pure water) is provided between adjacent separators of adjacentfuel cell units.

When fuel gas is supplied to the electrode reaction surface of the anodeelectrode, hydrogen is ionized here and moves to the cathode electrodevia the solid polymer electrolyte membrane. Electrons generated duringthis reaction are extracted to an external circuit and used as directcurrent electrical energy. Because oxidizing gas is supplied to thecathode electrode, hydrogen ions, electrons, and oxygen react togenerate water. Because heat is generated when water is created at theelectrode reaction surface, the electrode reaction surface is cooled bya cooling medium made to flow between the separators.

The fuel gas, oxidizing gas (generically known as reaction gas), and thecooling medium each need to flow through a separate flow passage.Therefore, sealing technology that keeps each flow passage sealed in afluid-tight or airtight condition is essential.

Examples of portions that must be sealed are: the peripheries of supplyports that are formed so as to penetrate the separators in the thicknessdirection thereof in order to supply and distribute reaction gas andcooling medium to each fuel cell unit of the fuel cell; the peripheriesof discharge ports that are formed so as to penetrate the separators inthe thickness direction thereof in order to collect and discharge thereaction gas and cooling medium that are discharged from each fuel cellunit; the outer peripheries of the electrode assemblies; and the spacebetween the separators of adjacent fuel cell units. Organic rubber thatis soft yet also has the appropriate resiliency or the like is employedas the material for the sealing member.

FIG. 35 is a plan view showing a conventional fuel cell stack. In FIG.35 the reference numeral 4 indicates a communication port such as a fuelgas supply port and discharge port, an oxidizing gas supply port anddischarge port, and a cooling medium supply port and discharge port thateach penetrate the fuel cell stack 1 in the direction in whichseparators 2 and 3 are stacked. The reference numeral 5 indicates anarea in which a plurality of fuel gas flow passages, oxidizing gas flowpassages, and cooling medium flow passages running along the separators2 and 3 are formed.

FIG. 36 is a longitudinal cross-sectional view of a conventional fuelcell stack 1 taken along the line X-X in FIG. 36. As can be seen in planview, in order to make the space occupied by the sealing member, thatdoes not contribute to power generation, as small as possible,conventionally, by locating gas sealing members 8 and 9, whichrespectively seal a fuel gas flow passage 6 and an oxidizing gas flowpassage 7, together with a cooling surface sealing member 10, whichseals a cooling medium flow passage, aligned in a row in the stackingdirection of the fuel cell units 11, the outer dimensions in thestacking direction of the fuel cell stack 1 are minimized.

According to FIG. 36, the fuel gas supply port 4 and the fuel gas flowpassage 6 that are isolated in a sealed state by the gas sealing members8 and 9 are connected by a communication path 12. The communication path12 is provided so as to detour around, in the thickness direction of theseparator 2, the gas sealing member 8 that seals the entire periphery ofthe fuel gas flow passage 6. More specifically, the communication path12 is formed in such a way that grooves are formed between the fuel gassupply port 4 and fuel gas flow passage 6 of the separator 2, and abridge plate 13 is provided over the grooves.

Moreover, the separator 3 also has a similar communication path (notshown) near the oxidizing gas communication port (not shown). Such astructure is disclosed in Japanese Unexamined Patent Application, FirstPublication No. Hei 10-74530.

However, because the bridge plate 13 is a separate element that isinstalled on the separator 2 so as to be substantially flush with theseparator 2, a gap 14 is inevitable between the separator 2 and bridgeplate 13 at a connecting portion therebetween, as shown in FIG. 37 (thesame description applies in the case of the separator 3). FIG. 37 is alongitudinal cross-sectional view, showing a conventional fuel cellstack 1, taken along the line Y-Y in FIG. 36. The drawback with thisstructure is that sealing performance may be lost if the gas sealingmembers 8 and 9 are deformed in the gap 14 when the gas sealing members8 and 9 are attached onto the separators 2 and 3 and the bridge plate13. Moreover, another drawback is that it is very difficult to form thegas sealing members 8 and 9 on the separators 2 and 3 and the bridgeplate 13, because the material of the gas sealing members 8 and 9 mayleak through the gap 14.

As disclosed in Japanese Unexamined Patent Application, FirstPublication No. 2001-148252 and U.S. Pat. No. 6,066,409, a technique inwhich through holes are formed in a separator that penetrate in thethickness direction of the separator, and a reaction gas is made to flowinto a gas flow passage via the through holes, has been proposed.However, in such a structure, a problem is experienced in that, becausereaction gas flow passages must be formed between the adjacentseparators not only on the front surface of the separator but also onthe rear surface thereof in order to allow the reaction gas to flow fromthe gas flow passage on the rear surface (cooling surface) to the gasflow passage on the front surface or vice versa, the thickness of thefuel cell units may be increased by the amount necessary to form theseflow passages.

Moreover, it is necessary to locate the cooling surface sealing memberso as to be offset inward (toward a reaction surface) from the gassealing member for ensuring a space to form the through paths in orderto allow the reaction gas to flow in from the rear surface of theseparator because the cooling surface sealing member that seals thecooling medium flow passage is provided on the rear surface of theseparator. As a result of locating the cooling surface sealing member soas to be offset from the gas sealing member, the cooling surface sealingmember is located at a position overlapping, as viewed in the stackingdirection, with the reaction gas flow passage that is located inwardfrom the gas sealing member. In this case, the minimum thickness of thefuel cell unit equals to the sum of the thickness of the reaction gasflow passage and the thickness of the cooling surface sealing member.Moreover, if the through holes are provided not only on the separatoradjacent to one electrode but also on the separator adjacent to theother electrode, the minimum thickness of the fuel cell is doubled. If afuel cell stack is formed by stacking a plurality of such fuel cellunits, the overall thickness of the fuel cell stack is found bymultiplying the number of stacks by the minimum thickness of each fuelcell unit, which makes it difficult to reduce the size of the fuel cellstack.

SUMMARY OF THE INVENTION

The present invention was conceived in view of the above circumstances,and it is an object thereof to provide a fuel cell whose dimension inthe stacking direction is restrained while ensuring sealing performance,and in which the sealing performance may be further improved by formingthe gas sealing member integrally with the separator. Another object ofthe present invention is to provide a separator of a fuel cell.

In order to solve the above problems, a first aspect of the presentinvention provides a fuel cell including a plurality of fuel cell units,each fuel cell unit including: an electrode assembly formed by disposingelectrodes on both sides of an electrolyte; a pair of separators thatsandwich the electrode assembly in the thickness direction thereof; andgas sealing members that are disposed at an outer peripheral portion ofthe electrode assembly, and that seal respective reaction gas flowpassages that are formed between each separator and the electrodeassembly and are bounded by the separators and electrode assembly,wherein, at least two of the fuel cell units that are stacked in thethickness direction thereof comprise at least two electrode assembliesand at least three separators that sandwich the electrode assemblies inthe thickness direction thereof, in each of the separators, reaction gascommunication ports that penetrate the separator in the thicknessdirection thereof are provided outward from the gas sealing members, inone of the separators of each of the fuel cell units, a through path isformed that penetrates the separator in the thickness direction thereofand connects one of the reaction gas communication ports with thereaction gas flow passages, and the through path formed in one of theseparators of one of the fuel cell units and the through path formed inone of the separators of adjacent one of the fuel cell units are offsetwith each other as viewed in the thickness direction of the separators.

According to the fuel cell as constructed above, because the number ofelements for cooling such as the cooling surface sealing member isreduced by the degree of reduction in the number of the cooling mediumflow passages, the manufacturing process may be simplified. In addition,because the separator need not be sufficiently thick to form the coolingmedium flow passage therein, the thickness of the fuel cell unit can bereduced, and consequently the thickness of the fuel cell stack can bereduced by the amount saved in this way.

According to the fuel cell as constructed above, in the one separator,because the reaction gas communication ports are connected with thereaction gas flow passages by the through paths, the reaction gascommunication paths need not be formed therein. Therefore, because a gapaccompanied with the communication paths may not be formed on the frontsurface (the surface forming the reaction gas flow passage) of theseparator, the portion, between the reaction gas communication ports andreaction gas flow passage, where the gas sealing member is formed can bemade flat. As a result, the leakage of the material of the gas sealingmember during formation thereof can be prevented, the deformation of thegas sealing member can be prevented, the gas sealing member can besecurely bonded to the predetermined position on the separator, and thusthe sealing performance of the gas sealing member is improved. Moreover,the reaction gas flow passage can be sealed in a fluid tight state bymaking the gas sealing member formed on the one separator and the gassealing member bonded to the electrolyte of the electrode assembly bepressed against the other separator.

In addition, in the other separator, the reaction gas need not flowalong the rear surface (the surface to be cooled) of this separatorbecause the reaction gas communication ports are connected with thereaction gas flow passage by the communication paths, accordingly, thecooling surface sealing member need not be formed at a positionoverlapping, as viewed in the stacking direction, with the reaction gasflow passage. As a result, by providing the cooling surface sealingmember so as to be offset, as viewed in the stacking direction, from thereaction gas flow passage, the dimensions of the fuel cell units,consequently, the dimensions of the fuel cell stack in the stackingdirection can be reduced by the amount saved by the above-mentionedoffset disposition.

Although the aforementioned gap is formed at a connecting portionbetween the other separator and the communication paths, the gap can besealed by making the gas sealing member bonded to the one separator andto the electrolyte be pressed against the gap.

In the fuel cell according to a second aspect of the present invention,a planar area of one electrode is larger than that of the otherelectrode.

According to the fuel cell as constructed above, a portion of theelectrolyte that extends out of the electrode (smaller electrode)contacting the one separator can be supported, in the thicknessdirection thereof, by the electrode (larger electrode) contacting theother separator. It is possible to bond the gas sealing member to theone separator so that the gas sealing member contacts the supportedportion of the electrolyte. As a result, the gas sealing member can bepressed against the electrolyte while ensuring the strength of theelectrolyte in the thickness direction thereof.

If the supported portion is made of sealing material instead of amaterial for the electrode, the sealing performance at the portion canbe further improved. The planar area of the electrolyte may be formedlarger than that of the larger electrode, or may be formed as large asthat of the larger electrode. If the planar area of the electrolyte islarger than that of the larger electrode, the gas sealing member may bebonded to the peripheral portion of the electrolyte.

The planar area of one electrode may be larger than that of the otherelectrode by at least an amount corresponding to the width of the gassealing member.

The planar area of one electrode may be larger than that of the otherelectrode, and the planar area of the one electrode and a planar areasurrounded by an outer periphery of the gas sealing member that isbonded to the one electrode may be substantially the same size as thatof the electrolyte.

The gas sealing member may be bonded to one of the separators that facesone of the electrodes and may be pressed against the electrode assembly.

According to the fuel cell as constructed above, by making the gassealing member be pressed against the electrode assembly, the leakage ofthe reaction gas from the space delimited by the electrode assembly canbe prevented, and by making the gas sealing member be pressed againstthe other separator, the leakage of the reaction gas to the outside canalso be prevented.

The gas sealing member may be bonded to one of the separators that facesone of the electrodes and may be pressed against one of the separatorsthat faces another of the electrodes.

The gas sealing member may be bonded to one of the separators that facesone of the electrodes and may be pressed against the electrode assemblyas well as against one of the separators that faces another of theelectrodes.

The gas sealing member may be bonded to the electrode assembly.

Two or more fuel cell units form a group of fuel cell units, and acooling medium flow passage for cooling the fuel cell units is formed inevery space between adjacent groups of fuel cell units, in one of theseparators of each of the groups of fuel cell units that forms thecooling medium flow passage, the through path is formed, in the other ofthe separators of each of the groups of fuel cell units that forms thecooling medium flow passage, a reaction gas communication path thatdetours around the gas sealing member in the thickness direction of theseparator and connects one of the reaction gas communication ports withthe reaction gas flow passages is formed, and both the through path andthe reaction gas communication path are formed in the separators of eachof the groups of fuel cell units that do not define the cooling mediumflow passage.

In the above fuel cell, the separators may be formed of carbon orstainless steel.

In the above fuel cell, at least two electrode assemblies may bedifferent in planar size.

The present invention further provides separators for sandwiching anelectrode assembly formed by disposing electrodes on both sides of anelectrolyte, including: reaction gas communication ports that penetratethe separators in the thickness direction thereof; and

through paths that penetrate the separators in the thickness directionthereof and connect the reaction gas communication ports with reactiongas flow passages that are formed between one of the separators and theelectrode assembly, wherein when the separators are stacked in thethickness direction thereof; at least two of the through paths areoffset with each other as viewed in the thickness direction of theseparators.

The separators may be integrated with the gas sealing member.

The separators may be formed of carbon or stainless steel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view schematically showing a fuel cellunit forming the fuel cell stack according to a first embodiment of thepresent invention.

FIG. 2 is a plan view showing an electrode assembly forming the fuelcell unit shown in FIG. 1.

FIG. 3 is a plan view showing a separator adjacent to one electrodeforming the fuel cell unit shown in FIG. 1.

FIG. 4 is a plan view showing a separator adjacent to the otherelectrode forming the fuel cell unit shown in FIG. 1.

FIG. 5 is a plan view showing the rear surface of the separator shown inFIG. 3.

FIG. 6 is a plan view showing the rear surface of the separator shown inFIG. 4.

FIG. 7 is a plan view showing a state in which the gas sealing member isprovided on the separator shown in FIG. 3.

FIG. 8 is a plan view showing a state in which the gas sealing member isprovided on the electrode assembly shown in FIG. 2.

FIG. 9 is a plan view showing a state in which the gas sealing member isprovided on the separator shown in FIG. 4.

FIG. 10 is a plan view showing a state in which the cooling surfacesealing member is provided on the separator shown in FIG. 5.

FIG. 11 is a plan view showing a state in which the cooling surfacesealing member is provided on the separator shown in FIG. 6.

FIG. 12 is a longitudinal cross-sectional view, showing the fuel cellstack shown in FIG. taken along the line A-A in FIG. 7.

FIG. 13 is a longitudinal cross-sectional view, showing the fuel cellstack shown in FIG. 1, taken along the line B-B in FIG. 7.

FIG. 14 is a longitudinal cross-sectional view, showing the fuel cellstack shown in FIG. 1, taken along the line C-C in FIG. 7.

FIG. 15 is a longitudinal cross-sectional view showing a secondembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 16 is a longitudinal cross-sectional view showing the secondembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 17 is a longitudinal cross-sectional view showing a thirdembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 18 is a longitudinal cross-sectional view showing the thirdembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 19 is a longitudinal cross-sectional view showing a fourthembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 20 is a longitudinal cross-sectional view showing the fourthembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 21 is a longitudinal cross-sectional view showing a fifthembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 22 is a longitudinal cross-sectional view showing the fifthembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 23 is a longitudinal cross-sectional view showing a sixthembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 24 is a longitudinal cross-sectional view showing the sixthembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 25 is a longitudinal cross-sectional view showing a seventhembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 26 is a longitudinal cross-sectional view showing the seventhembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 27 is a longitudinal cross-sectional view showing an eighthembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 28 is a longitudinal cross-sectional view showing the eighthembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 29 is a longitudinal cross-sectional view showing a ninthembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 30 is a longitudinal cross-sectional view showing the ninthembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 31 is a longitudinal cross-sectional view showing a tenthembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 32 is a longitudinal cross-sectional view showing the tenthembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 33 is a longitudinal cross-sectional view showing an eleventhembodiment of the present invention, corresponding to FIG. 12 showingthe first embodiment.

FIG. 34 is a longitudinal cross-sectional view showing the eleventhembodiment of the present invention, corresponding to FIG. 13 showingthe first embodiment.

FIG. 35 is a plan view schematically showing a fuel cell unit in aconventional fuel cell stack.

FIG. 36 is a longitudinal cross-sectional view, showing the vicinity ofa fuel gas supply port in the fuel cell stack shown in FIG. 35, takenalong the line X-X.

FIG. 37 is a longitudinal cross-sectional view, showing the majorportion of the vicinity of the fuel gas supply port in the fuel cellstack shown in FIG. 36, taken along the line Y-Y.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fuel cell stack according to an embodiment of the present inventionwill now be described in detail with reference to the drawings.

As shown in FIG. 12, the fuel cell stack 20 according to the presentembodiment is formed by stacking a plurality of fuel cell units 21. Asshown in FIG. 1, the fuel cell unit 21 is formed by sandwiching anelectrode assembly 22 between a pair of separators 23 and 24. Betweenthe electrode assembly 22 and each of the separators 23 and 24 aredisposed respectively gas sealing members 25 and 26. As shown in FIGS.12 and 13, these gas sealing members 25 and 26 delimit a fuel gas flowpassage 27 and an oxidizing gas flow passage 28 so as to seal them oneither side of the electrode assembly 22.

As shown in FIGS. 2 and 12, the electrode assembly 22 has, for example,a solid polymer electrolyte membrane 29 (hereinafter simply referred toas an electrolyte membrane) formed from a perfluorosulfonate polymer,and an anode electrode 30 and cathode electrode 31 that sandwich twosurfaces of the electrolyte membrane 29.

As shown in FIG. 2, for example, the electrolyte membrane 29 has aplurality of through holes 32. The electrolyte membrane 29 is theequivalent size to the separators 23 and 24 that are described below,and each of the through holes 32 is placed at a position thatcorresponds to the respective supply ports 33 to 35 and the respectivedischarge ports 36 to 38 of the separators 23 and 24.

The anode electrode 30 and the cathode electrode 31 are constructed, forexample, by stacking catalyst layers, formed from an alloy having Pt(platinum) as the main constituent, on a surface of a gas diffusionlayer formed from porous carbon cloth or porous carbon paper thatcontacts the electrolyte membrane 29.

The fuel cell unit 21 includes two types of separators 23 and 24. Asshown in FIGS. 3 and 4, each of the separators 23 and 24 is formed from:corrugated portions 39 and 40 made up of a plurality of indentations andbumps that have a fixed height and are formed in a fixed pattern byscraping out a plurality of grooves (not shown) in a surface of a flatplate made from carbon; a fuel gas supply port (reaction gascommunication port) 33, an oxidizing gas supply port (reaction gascommunication port) 34, a cooling medium supply port (cooling mediumcommunication port) 35, a fuel gas discharge port (reaction gascommunication port) 36, an oxidizing gas discharge port (reaction gascommunication port) 37, and a cooling medium discharge port (coolingmedium communication port) 38 that each penetrate the two separators 23and 24 so as to make possible both the supply and discharge of fuel gas(for example, hydrogen gas), oxidizing gas (for example, air thatcontains oxygen), and a cooling medium (for example, pure water)respectively that are made to flow through the corrugated portions 39and 40; and planar portions 41 and 42 that are disposed so as tosurround each of the supply ports 33 to 35, the discharge ports 36 to38, and the corrugated portions 39 and 40.

As shown in FIGS. 3 and 4, the cooling medium supply port 35 and thecooling medium discharge port 38 are located substantially in the centerin the transverse direction of the separators 23 and 24 (i.e., thedirection indicated by the arrow P). The fuel gas supply port 33 and theoxidizing gas supply port 34 are located at both sides in the transversedirection of the separators 23 and 24 (i.e., the direction indicated bythe arrow P) sandwiching the cooling medium supply port 35. Furthermore,the fuel gas discharge port 36 and the oxidizing gas discharge port 37are located at both sides in the transverse direction of the separators23 and 24 (i.e., the direction indicated by the arrow P) sandwiching thecooling medium discharge port 38. The fuel gas discharge port 36 and theoxidizing gas discharge port 37 are located at diagonally oppositepositions respectively to the fuel gas supply port 33 and the oxidizinggas supply port 34.

The lengths (as indicated by the arrow R) of the fuel gas supply port 33and discharge port 36 and the lengths of the oxidizing gas supply port34 and discharge port 37 in the longitudinal directions of theseparators 23 and 24 (the direction indicated by the arrow Q) are madeto be shorter than the lengths (as indicated by the arrow S) of theadjacent cooling medium supply port 35 and discharge port 38. As aresult, the size of the space (as indicated by the arrow T) from thefuel gas supply port 33 and discharge port 36 and from the oxidizing gassupply port 34 and discharge port 37 to the corrugated portions 39 and40 is made larger than the size of the space (as indicated by the arrowU) from the cooling medium supply port 35 and discharge port 38 to thecorrugated portions 39 and 40.

One ends 44 of through paths 43 open in one surface (the surface facingthe fuel gas) of the separator 23 for one electrode out of the pair ofseparators 23 and 24, as shown in FIG. 3. These through paths 43 areformed so as to penetrate the separator 23 in the thickness directionthereof and so as to connect the fuel gas supply port 33 with thecorrugated portion 39, and to connect the corrugated portion 39 with thefuel gas discharge port 36, respectively.

On the other hand, as shown in FIG. 4, in one surface (the surfacefacing the oxidizing gas) of the other separator 24 for the otherelectrode, there are provided oxidizing gas communication paths 46between the oxidizing gas supply port 34 and the corrugated portion 40,and between the corrugated portion 40 and the oxidizing gas dischargeport 37, respectively, which allow the oxidizing gas supplied from theoxidizing gas supply port 34 to flow through the corrugated portion 40,and which allow the oxidizing gas that has passed through the corrugatedportion 40 to be discharged from the oxidizing gas discharge port 37.Each of the oxidizing gas communication paths 46 comprises a pluralityof grooves 47 that are formed on one surface of the separator 24, and aplanar bridge plate 48 that extends right across the grooves 47. On thesurface of the separator 24 where the bridge plate 48 is placed isformed a recess 49 into which the bridge plate 48 is fitted. This recess49 enables the surface of the bridge plate 48 to be placed within thesame planar surface as the surface 42 of the separator 24.

In the other surfaces (the surfaces facing the cooling medium) of theseparators 23 and 24, there are provided cooling medium communicationpaths 50 that connect the cooling medium supply port 35 with thecorrugated portions 39 and 40, and there are provided cooling mediumcommunication paths 50 that connect the corrugated portions 39 and 40with the cooling medium discharge port 38, as shown in FIG. 5 or FIG. 6.Moreover, as shown in FIG. 5, the other ends 45 of the through paths 43open in the other surface of the separator 23 for the one electrode.Furthermore, as shown in FIGS. 3 and 5, the one ends 44 of the throughpaths 43 are located toward the corrugated portion 39, and the otherends 45 of the through paths 43 are located toward the fuel gas supplyport 33 or fuel gas discharge port 36. Note that the surface of theseparator 24, shown in FIG. 6, for the other electrode is constructed inthe same way as the other surface of the separator 23 shown in FIG. 5except that the through paths 43 are not formed therein.

As shown in FIGS. 7 and 9, the gas sealing members 25 and 26 thatrespectively seal the reaction gas flow passages are integrally formedsuch that a plurality of sub-loop portions 53 (53 a to 53 c) thatencircle each of the supply ports 33 to 35 and discharge ports 36 to 38are disposed on both sides of main-loop portions 51 and 52 that encirclethe outer peripheries of the corrugated portions 39 and 40.

FIGS. 7 and 9 respectively show a state in which the gas sealing member25 is provided on the anode electrode surface of the separator 23, and astate in which the gas sealing member 26 is provided on the cathodeelectrode surface of the separator 24.

According to FIGS. 7 and 9, the main-loop portions 51 and 52 of the gassealing members 25 and 26 are positioned so as to run along the planarportions 41 and 42 between the respective supply ports 33 to 35 and thecorrugated portions 39 and 40, and between the respective dischargeports 36 to 38 and the corrugated portions 39 and 40.

The portions of the main-loop portion 51 of the gas sealing member 25that seals the fuel gas supply port 33 or fuel gas discharge port 36 arepositioned so as to be offset from the one ends 44 of the through paths43 toward the fuel gas supply port 33 or fuel gas discharge port 36 sothat the one ends 44 of the through paths 43 are not covered by the gassealing member 25. The gas sealing member 25 is bonded to the separatorso as to be integrated therewith.

On the other hand, the main-loop portion 52 of the gas sealing member 26is positioned so as to run on the bridge plates 48 provided in thecommunication paths 46 so that, between the supply ports 33 to 35 andthe corrugated portion 40, and between the discharge ports 36 to 38 andthe corrugated portion 40, fluid flow is allowed only through thegrooves 47 formed in the communication paths 43, and the other portionsare sealed in a fluid tight state.

FIG. 8 shows a state in which the gas sealing members 25 and 26 areprovided on the electrode assembly 22. As shown in FIG. 8, the gassealing members 25 and 26 are provided on the solid polymer electrolytemembrane 29. The gas sealing member 26 is integrated with the solidpolymer electrolyte membrane 29.

As shown in FIG. 12, a plurality of fuel cell units 21 thus formed arestacked with respect to each other while sandwiching cooling surfacesealing members 55 therebetween. As shown in FIGS. 10 and 11, thecooling surface sealing member 55 is formed by integrally connectingmain-loop portion 57 and sub-loop portions 58.

The main-loop portion 57 of the cooling surface sealing member 55 runsbetween the supply ports 33 and 34 of the fuel gas and oxidizing gas andthe corrugated portions 39 or 40, and also between the discharge ports36 and 37 and the corrugated portions 39 and 40, and seals the peripheryof the cooling medium flow passage 61 that is formed by connecting thecooling medium supply port 35 to the corrugated portions 39 and 40 viathe communication paths 50, and by connecting the corrugated portions 39and 40 to the cooling medium discharge port 38 via the communicationpaths 50. Moreover, the sub-loop portions 58 of the cooling surfacesealing member 55 independently seal each of the fuel gas and oxidizinggas supply ports 33 and 34 and discharge ports 36 and 37.

As shown in FIG. 10, the portions of the main-loop portion 57 of thecooling surface sealing member 55 that seals the peripheries of the fuelgas supply port 33 or fuel gas discharge port 36 are positioned so as tobe offset from the other ends 45 of the through paths 43 toward thecorrugated portion 39 so that the other ends 44 of the through paths 43are not covered by the cooling surface sealing member 55. As a result,the fuel gas that is supplied from the fuel gas supply port 33 and isdischarged through the fuel gas discharge port 36 flows through theother ends 45 of the through paths 43 without flowing through thecorrugated portion 39 on the cooling surface. As mentioned above,because the one ends 44 of the through paths 43 are not covered by thegas sealing member 25, it is possible to supply or discharge the fuelgas via the one ends 44.

A cross section of a portion of the fuel cell stack 20 that isconstructed in this manner is shown in FIG. 12. FIG. 12 is alongitudinal cross-sectional view, showing the fuel cell stack 20 shownin FIG. 1, taken along the line A-A in FIG. 7. In FIG. 12, there isshown a flow passage that allows the fuel gas to flow into the fuel gasflow passage 27. Moreover, the gas sealing members 25 and 26 that eachseal the space between the electrode assembly 22 and the separator 23and the space between the electrode assembly 22 and the separator 24 aredisposed so as to sandwich the electrolyte membrane 29 in the thicknessdirection thereof at positions corresponding to each other as viewed inthe stacking direction. As can be seen in FIG. 12, the fuel gas that issupplied from the fuel gas supply port 33 on the exterior side of themain-loop portion 51 of the gas sealing member 25 is allowed to flowinto the fuel gas flow passage 27 on the interior side of the main-loopportion 51 of the gas sealing member 25 via the through paths 43 thatpenetrate the separator 23 in the thickness direction thereof. Becausethe reaction gas communication paths that detour around the gas sealingmember 25 in the thickness direction need not be formed in the separator23, and because the bridge plate is not necessary, it is possible toensure the flatness of the portion where the gas sealing member 25 isdisposed. Accordingly, the sealing performance of the gas sealing member25 can be improved because the gas sealing member 25 can be reliablybonded to a predetermined portion of the separator 23 so as to beintegrated therewith while preventing the deformation of the gas sealingmember 25 when it is integrally formed on the separator 23.

Although, the above description is for the fuel gas supply port 33, thesame description also applies in the case of the fuel gas discharge port36.

FIG. 13 is a longitudinal cross-sectional view, showing the fuel cellstack 20 shown in FIG. 1, taken along the line B-B in FIG. 7. As can beseen in FIG. 13 as well, the gas sealing members 25 and 26 that eachseal the space between the electrode assembly 22 and the separator 23and the space between the electrode assembly 22 and the separator 24 aredisposed so as to sandwich the electrolyte membrane 29 in the thicknessdirection thereof at positions corresponding to each other as viewed inthe stacking direction. The oxidizing gas communication paths 46 detouraround the main-loop portion 52 of the gas sealing member 26 in thethickness direction of the separator 24, and connect the interior of themain-loop portion 52 of the gas sealing member 26 with the exteriorthereof so as to allow the oxidizing gas that is supplied from theoxidizing gas supply port 34 on the exterior side of the main-loopportion 52 of the gas sealing member 26 to flow into the oxidizing gasflow passage 28 on the interior side of the main-loop portion 52 of thegas sealing member 26. As a result, the oxidizing gas need not flow onthe rear surface (cooling surface) of the separator 24, and the coolingsurface sealing member 55 need not be provided so as to overlap with theoxidizing gas flow passage 28 as viewed in the stacking direction.

Although, the above description is for the oxidizing gas supply port 34,the same description also applies in the case of the oxidizing gasdischarge port 37.

FIG. 14 is a longitudinal cross-sectional view, showing the fuel cellstack 20 shown in FIG. 1, taken along the line C-C in FIG. 7. In FIG.14, there is shown a flow passage that connects the cooling mediumsupply port 35 with the cooling medium flow passage 61 that is delimitedbetween adjacent fuel cell units 21.

As explained above, in the present embodiment, because the gas sealingmember 25 can be reliably bonded to a predetermined portion of theseparator 23 that does not include the communication paths so as to beintegrated therewith while preventing the deformation of the gas sealingmember 25 when it is formed, the sealing performance of the gas sealingmember 25 can be improved. Moreover, because the reaction gases (fuelgas and oxidizing gas) need not flow through the rear surface (coolingsurface) of the separator 24 for the other electrode, the coolingsurface sealing member 55 need not be provided so as to overlap with theoxidizing gas flow passage 28 as viewed in the stacking direction.Therefore, the dimensions of the fuel cell unit 21 in the stackingdirection can be reduced by the amount saved in this way, andconsequently the dimensions in the stacking direction of the fuel cellstack 20 that is formed by stacking the fuel cell units 21 can begreatly reduced.

Next, FIGS. 15 and 16 show the second embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. For the elements in the following embodiments whichare common in the previous embodiment, the same reference symbols willbe applied, and explanations thereof will be omitted as appropriate.

In the second embodiment, the planar area of the cathode electrode 31 ismade larger than that of the anode electrode 30 so that one peripheraledge of the gas sealing member 26 that is bonded to the electrolytemembrane 29 so as to be integrated therewith contacts the cathodeelectrode 31. Accordingly, because the surface of the electrolytemembrane 29 to which the gas sealing member 26 is bonded is reinforcedin the thickness direction by the cathode electrode 31, the reliabilityof the fuel cell stack 20 can be improved. Furthermore, because theentire surface of the electrolyte membrane 29 facing the oxidizing gasis covered with the cathode electrode 31, and thus the electrolytemembrane 29 is not exposed to the oxidizing gas at all, the electrolytemembrane 29 is reinforced over the entire surface thereof, andconsequently, the durability of the electrolyte membrane 29 can befurther improved. As in the first embodiment, in this embodiment aswell, it is possible to reduce the dimensions of the fuel cell stack 20in the stacking direction while ensuring the sealing performance of thegas sealing member 25. Note that the planar area of the cathodeelectrode 31 is made larger than that of the anode electrode 30 in thisembodiment; however, the planar area of the anode electrode 30 may bemade larger than that of the cathode electrode 31, instead.

Next, FIGS. 17 and 18 show the third embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. In the third embodiment, the gas sealing member 25 isprovided as a double sealing structure. That is, the gas sealing member25 is bonded to the separator 23 for the one electrode so as to beintegrated therewith, and the gas sealing member 25 is pressed againstthe electrolyte membrane 29 of the electrode assembly 22 as well asagainst the separator 24 for the other electrode. Accordingly, becausethe gas sealing member 25 is pressed against the electrolyte membrane29, flowing out of the fuel gas from the space delimited by theelectrode assembly 22 can be prevented, and at the same time, becausethe gas sealing member 25 is pressed against the separator 24 for theother electrode, flowing out of the fuel gas to the outside can bereliably prevented. As in the first embodiment, in this embodiment aswell, it is possible to improve the sealing performance by ensuring thesealing function of the gas sealing member 25. In addition, because thegas sealing member 25 is provided only on the separator 23 for the oneelectrode so as to be integrated therewith, the gas sealing member 25can be formed in one process, and need not be formed on the otherseparator 24, which simplifies the manufacturing process. Moreover, asshown in FIG. 18, because the main-loop portion 57 of the coolingsurface sealing member 55 is positioned so as to be offset from themain-loop portion 51 of the gas sealing member 25 in the vicinity of theoxidizing gas supply port 34 (as well as in the vicinity of theoxidizing gas discharge port 37), the thickness of each of the fuel cellunits 21 in the stacking direction can be reduced by the amount saved inthis way, and consequently the thickness of the fuel cell stack 20 canbe greatly reduced. Note that the sealing structure is not limited to adouble sealing structure, and a multiple sealing structure formed bythree or more seals may be employed. Because the main-loop portion 57 ofthe cooling surface sealing member 55 is disposed toward outside, thedimensions of the fuel cell stack 20 in the stacking direction can befurther reduced.

Next, FIGS. 19 and 20 show the fourth embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. In the fourth embodiment, the cathode electrode 31 ismade as large as the electrolyte membrane 29 that is made larger thanthe anode electrode 30, and merely the gas sealing member 25 that isbonded to the separator 23 for the one electrode so as to be integratedtherewith is employed as a gas sealing member. The gas sealing member 25is pressed against the electrolyte membrane 29 as well as against theseparator 24 for the other electrode. In this embodiment, because thestrength of the electrode assembly 22 in the thickness direction thereofcan be increased by reinforcing the electrolyte membrane 29 using thecathode electrode 31, the gas sealing member 25 can be pressed againstthe electrolyte membrane 29 with more pressure, whereby the sealingperformance can be further increased. Moreover, as in the firstembodiment, in this embodiment as well, it is possible to reduce thedimensions of the fuel cell stack 20 in the stacking direction whileimproving the sealing performance by ensuring the sealing function ofthe gas sealing member 25. Furthermore, because the durability of theelectrolyte membrane 29 can be improved as in the second embodiment, thereliability of the fuel cell stack 20 can also be improved.

flow passage for fuel gas (e.g., hydrogen) on the surface of the anodeside separator that is positioned facing the anode electrode, and thereis provided a flow passage for oxidizing gas (for example, air thatcontains oxygen) on the surface of the cathode side separator that ispositioned facing the cathode electrode.

Next, FIGS. 21 and 22 show the fifth embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. In the fourth embodiment, the cooling medium flowpassage 61 is formed for every two fuel cell units 21, and cooling isperformed on every two cells (i.e., two fuel cell units). The fuel cellstack 20 in this embodiment includes a separator 62 that does notcontribute to forming the cooling medium flow passage 61. The oxidizinggas (e.g., air that contains oxygen) flows along one surface of theseparator 62, and the fuel gas (e.g., hydrogen) flows along the othersurface of the separator 62. As shown in FIG. 21, the through path 43(for the reaction gas, e.g., for the fuel gas) formed in the separator62 (one of the separators of one of the fuel cell units 21) is locatedso as to be offset, as viewed in the stacking direction, with respect tothe through path 43 (for the same reaction gas, e.g., for the fuel gas)formed in the separator 23 (one of the separators of adjacent one of thefuel cell units 21). Accordingly, because the number of elements forcooling such as the cooling surface sealing member 55 is reduced by thedegree of reduction in the number of the cooling medium flow passages61, the manufacturing process may be simplified. In addition, becausethe separator 62 need not be sufficiently thick to form the coolingmedium flow passage 61 therein, the thickness of the fuel cell unit 21can be reduced, and consequently the thickness of the fuel cell stack 20can be reduced by the amount saved in this way. Furthermore, as in thefirst embodiment, in this embodiment as well, it is possible to reducethe dimensions of the fuel cell stack 20 in the stacking direction whileimproving the sealing performance by ensuring the sealing function ofthe gas sealing member 25. Note that, in this embodiment, a descriptionis given of when cooling is performed for every two fuel cell units;however, the present invention is not limited to this and the fuel cellstack 20 may also be structured such that cooling is performed for everythree or more fuel cell units 21.

Although not shown in the drawings, if cooling is performed for everythree or more fuel cell units 21, the separators are configured suchthat the through paths 43 formed in two or more separators are locatedso as to be offset with respect to each other, as viewed in the stackingdirection. For example, if cooling is performed for every three fuelcell units 21, two separators 62 and one separator 23 are included inthree fuel cell units 21, and through paths 43 are formed at threepositions, as viewed in the stacking direction.

Note that, in this embodiment, only one of the reaction gases (e.g., thefuel gas) is supplied through the through paths 43; however, it ispossible to configure the fuel cell units 21 in such a manner that bothof the reaction gases are supplied through the through paths 43.

Next, FIGS. 23 and 24 show the sixth embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. In the sixth embodiment, cooling is performed on everytwo fuel cell units as in the fifth embodiment, and the cathodeelectrode 31 is made as large as the electrolyte membrane 29 as in thefourth embodiment, furthermore, the gas sealing member 25 is pressedagainst the electrolyte membrane 29 of the electrode assembly 22 as wellas against the separator 24 for the other electrode. Accordingly, as inthe fifth embodiment, the manufacturing process may be simplified.Moreover, as in the fourth embodiment, because the gas sealing member 25can be pressed against the electrolyte membrane 29 with more pressure,the sealing performance can be further increased. Furthermore, as in thefirst embodiment, in this embodiment as well, it is possible to reducethe dimensions of the fuel cell stack 20 in the stacking direction whileimproving the sealing performance by ensuring the sealing function ofthe gas sealing member 25.

Next, FIGS. 25 and 26 show the seventh embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. In the seventh embodiment, the separators 23 and 24are provided with corrugated portions 39 and 40, supply ports 33 to 35,discharge ports 36 to 38, and planar sections 41 and 42, as shown inFIG. 1, by press forming a stainless steel plate with a plate thicknessof approximately 0.1 to 0.5 mm. By using press formed separators 24 and25, the thicknesses of the separators may be reduced, and alsoproductivity can be improved. As in the second embodiment, because theplanar area of the cathode electrode 31 is made larger than that of theanode electrode 30, the surface of the electrolyte membrane 29 to whichthe gas sealing member 26 is bonded is reinforced in the thicknessdirection by the cathode electrode 31; therefore, the reliability of thefuel cell stack 20 can be improved. Furthermore, as in the firstembodiment, in this embodiment as well, it is possible to reduce thedimensions of the fuel cell stack 20 in the stacking direction whileimproving the sealing performance by ensuring the sealing function ofthe gas sealing member 25.

Next, FIGS. 27 and 28 show the eighth embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. As in the seventh embodiment, in this embodiment aswell, the separators 23 and 24 are made by press forming stainless steelplates. Moreover, as in the third embodiment, in this embodiment aswell, because the gas sealing member 25 is pressed against theelectrolyte membrane 29 of the electrode assembly 22 as well as againstthe separator 24 for the other electrode, flowing out of the reactiongases to the outside can be reliably prevented. Furthermore, as in thefirst embodiment, in this embodiment as well, it is possible to reducethe dimensions of the fuel cell stack 20 in the stacking direction whileimproving the sealing performance by ensuring the sealing function ofthe gas sealing member 25.

Next, FIGS. 29 and 30 show the ninth embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. As in the seventh embodiment, in this embodiment aswell, the separators 23 and 24 are made by press forming stainless steelplates. Moreover, as in the fourth embodiment, in this embodiment aswell, the cathode electrode 31 is made as large as the electrolytemembrane 29, and the gas sealing member 25 is pressed against theelectrolyte membrane 29 as well as against the separator 24 for theother electrode; therefore, the sealing performance can be increased.Furthermore, as in the first embodiment, in this embodiment as well, itis possible to reduce the dimensions of the fuel cell stack 20 in thestacking direction while improving the sealing performance by ensuringthe sealing function of the gas sealing member 25.

Next, FIGS. 31 and 32 show the tenth embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. As in the seventh embodiment, in this embodiment aswell, the separators 23 and 24 are made by press forming stainless steelplates. Moreover, because cooling is performed on every two fuel cellunits, the manufacturing process may be simplified, and the dimensionsof the fuel cell stack 20 in the stacking direction can be reduced.Furthermore, as in the first embodiment, in this embodiment as well, itis possible to reduce the dimensions of the fuel cell stack 20 in thestacking direction while improving the sealing performance by ensuringthe sealing function of the gas sealing member 25.

Next, FIGS. 33 and 34 show the eleventh embodiment of the presentinvention, respectively corresponding to FIGS. 12 and 13 showing thefirst embodiment. As in the seventh embodiment, in this embodiment aswell, the separators 23 and 24 are made by press forming stainless steelplates. Moreover, the cathode electrode 31 is made as large as theelectrolyte membrane 29 as in the sixth embodiment. Accordingly, themanufacturing process may be simplified, and the dimensions of the fuelcell stack 20 in the stacking direction may be reduced. Moreover,because the gas sealing member 25 can be pressed against the electrolytemembrane 29 with more pressure, the sealing performance can beincreased. Furthermore, as in the first embodiment, in this embodimentas well, it is possible to reduce the dimensions of the fuel cell stack20 in the stacking direction while improving the sealing performance byensuring the sealing function of the gas sealing member 25.

INDUSTRIAL APPLICABILITY

As explained above, according to the fuel cell stack in the first aspectof the present invention, because the gas sealing member can be securelybonded to the predetermined position on the separator while preventingdeformation of the gas sealing member during formation thereof, thesealing performance of the gas sealing member is improved. Moreover, inthe other separator, the reaction gas need not flow along the rearsurface (the surface to be cooled) of this separator, and the coolingsurface sealing member need not be formed at a position overlapping withthe reaction gas flow passage, i.e., the cooling surface sealing membermay be located so as to be offset, as viewed in the stacking direction,from the reaction gas flow passage. Therefore, the dimensions of thefuel cell stack in the stacking direction can be reduced by the amountsaved by the above-mentioned offset disposition.

According to the fuel cell stack in the second aspect of the presentinvention, because the gas sealing member can be pressed against theelectrolyte while ensuring the strength of the electrolyte in thethickness direction thereof, the durability of the electrolyte can beimproved, and consequently the reliability of the fuel cell stack can beimproved.

According to the fuel cell stack in the third aspect of the presentinvention, because the gas sealing member that is bonded to the oneseparator and that has a sufficient sealing performance is pressedagainst the electrode assembly as well as against the other separator,flowing out of the reaction gases to the outside can be reliablyprevented by the gas sealing member, and consequently the reliability ofthe fuel cell stack can be improved.

1. A fuel cell comprising a plurality of fuel cell units, each fuel cellunit comprising: an electrode assembly formed by disposing electrodes onboth sides of an electrolyte; a pair of separators that sandwich theelectrode assembly in the thickness direction thereof; and gas sealingmembers that are disposed at an outer peripheral portion of theelectrode assembly, and that seal respective reaction gas flow passagesthat are formed between each separator and the electrode assembly andare bounded by the separators and electrode assembly, wherein, at leasttwo of the fuel cell units that are stacked in the thickness directionthereof comprise at least two electrode assemblies and at least threeseparators that sandwich the electrode assemblies in the thicknessdirection thereof, in each of the separators, reaction gas communicationports that penetrate the separator in the thickness direction thereofare provided outward from the gas sealing members, in one of theseparators of each of the fuel cell units, a through path is formed thatpenetrates the separator in the thickness direction thereof and connectsone of the reaction gas communication ports with the reaction gas flowpassages, and the through path formed in one of the separators of one ofthe fuel cell units and the through path formed in one of the separatorsof adjacent one of the fuel cell units are offset with each other asviewed in the thickness direction of the separators.
 2. The fuel cellaccording to claim 1, wherein, in the electrodes forming the electrodeassembly, a planar area of one electrode is larger than that of theother electrode.
 3. The fuel cell according to claim 2, wherein, in theelectrodes forming the electrode assembly, a planar area of oneelectrode is larger than that of the other electrode by at least anamount corresponding to the width of the gas sealing member.
 4. The fuelcell according to claim 1, wherein, in the electrodes forming theelectrode assembly, a planar area of one electrode is larger than thatof the other electrode, and the planar area of the one electrode and aplanar area surrounded by an outer periphery of the gas sealing memberthat is bonded to the one electrode are substantially the same size asthat of the electrolyte.
 5. The fuel cell according to claim 1, whereinthe gas sealing member is bonded to one of the separators that faces oneof the electrodes and is pressed against the electrode assembly.
 6. Thefuel cell according to claim 1, wherein the gas sealing member is bondedto one of the separators that faces one of the electrodes and is pressedagainst one of the separators that faces another of the electrodes. 7.The fuel cell according to claim 1, wherein the gas sealing member isbonded to one of the separators that faces one of the electrodes and ispressed against the electrode assembly as well as against one of theseparators that faces another of the electrodes.
 8. The fuel cellaccording to claim 1, wherein the gas sealing member is bonded to theelectrode assembly.
 9. The fuel cell according to claim 1, wherein twoor more fuel cell units form a group of fuel cell units, and a coolingmedium flow passage for cooling the fuel cell units is formed in everyspace between adjacent groups of fuel cell units, in one of theseparators of each of the groups of fuel cell units that forms thecooling medium flow passage, the through path is found, in the other ofthe separators of each of the groups of fuel cell units that forms thecooling medium flow passage, a reaction gas communication path thatdetours around the gas sealing member in the thickness direction of theseparator and connects one of the reaction gas communication ports withthe reaction gas flow passages is formed, and both the through path andthe reaction gas communication path are formed in the separators of eachof the groups of fuel cell units that do not define the cooling mediumflow passage.
 10. The fuel cell according to claim 1, wherein theseparators are formed of carbon or stainless steel.
 11. The fuel cellaccording to claim 1, wherein the at least two electrode assemblies aredifferent in planar size.
 12. Separators for sandwiching an electrodeassembly formed by disposing electrodes on both sides of an electrolyte,comprising: reaction gas communication ports that penetrate theseparators in the thickness direction thereof; and through paths thatpenetrate the separators in the thickness direction thereof and connectthe reaction gas communication ports with reaction gas flow passagesthat are formed between one of the separators and the electrodeassembly, wherein when the separators are stacked in the thicknessdirection thereof, at least two of the through paths are offset witheach other as viewed in the thickness direction of the separators. 13.The separators according to claim 12, wherein the separators areintegrated with the gas sealing member.
 14. The separators according toclaim 12, wherein the separators are formed of carbon or stainlesssteel.